Piezo electric crystal



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,y I. wzo ELECTRIC CRYSTAL VFiled oct.l1`4, 1925 gva/vanto@ Guam,

Patented Aug. 13, 1929.

UNITED STATES PATENT OFFICE.

ALBERT II. TAYLOR AND ALFRED cnossLnY, OF WASHINGTON, DISTRICT or COLUM- BIA, AssIcNons To WIRED RADIO, ING., or NEW YORK, N. Y., A CORPORATION F DELAWARE.

PIEZO ELECTRIC CRYSTAL.

Application filed October 14, 1925.

Our invention relates broadly to piezo electric crystals and more particularly to a construction of piezo electric crystal which may be produced at relatively small cost having maximum power output.

One of the objects of our invention is to provide a system for grinding piezo electric crystals according to a definite law, by which a piezo electric crystal having maximum piezo electric effect may be produced.

Another object of our invention is to provide a construction of piezo electric crystal y' wherein the crystal is cut with one of its geometrical axes at a zero angle to the opwith the principles of our invention; and

F ig. 2 is a view showing the theoretical principles involved in our invention.

Our invention resides in the cutting of piezo electric crystals with one of the geometrical axes thereof at a zero angle to the optical axis of the natural crystalline body from which the crystals are produced. The individual crystals are cut from the original crystal in such manner that the optical axis is exactly parallel to a plane which contains either side of the crystal along one dimension, as shown in Fig. l at c c. In Fig. l, I have represented the three geometrical axes of the crystal that is the optical axis c c and the axes a a and b b which are the two electrical axes along which piezo elect-ric propertiesare exhibited. In Zero angle crystals the Z) b axis is at right angles to the axis c c and the axis a a is perpendicular to the plane of the faces of the crystal.

Having cut the crystal along the optical axis in such manner that one side is disposed parallel to the optical axis, We have discovered that the maximum radio fre- Y quency oscillatory Output or piezo electric effect of the crystal can be obtained from the Serial No. 62,472.

crystal when two of the geometrical axes are ground to dimensions which bear a mathematical ratio to each other equal to a whole number. That is to say a a dimension should be ground to be an inegral part of b b dimension or vice versa, for maximum output from the crystal. An example of this case may be given as follows: a crystal having dimension of five millimeters alon T the a axis, dimension of twenty-two milli-J meters along the b b axis, and a dimension of twenty-live millimeters along the c c axis, is ground on the b b axis until the b b axis is reduced to twenty millimeters at which dimension maximum output or greatest piezo electric effect will be obtained from the crvstal. I dimension of the b'b axis is exactly four tim-cs the dimension of the a a axis when maximum Output is obtained. The dimension along the b b axis could also be reduced to ten or fifteen millimeters, and at each of these dimensions the maximum output relationship is noted when a mathematical ratio b b of @equal to a whole number is obtained.

It is also necessary at times to grind the crystal down on the c c axis to increase Output and to correct for single frequency, that 1s to say to secure a crystal which is capable of oscillating freely at one and only one frequency, and in some cases to malte the c c axis also equal to an integral times the a a axis dimension, that is, by grinding the c c dimension to a value equal to c cz. i

In Fig. l of the drawings we have shown the piezo electric crystal ground along the l) axis from an original b I) dimension to a l) by dimension, in order to secure a whole number relationship between b by and the thickness dimension ai a.

Reference is made to Fig. 2 in order to explain the reasons for the desirable integral relationship of the dimensions 0r. (a and l) b for securing the increased output from the crystal. The crystal may be likened to an open and organ pipe, indicated by reference character 1, which has been so built as to be resonant to a definite sound wave. In this pipe a standing sound wave, indicated by reference character 2, may be produced.

In the drawing the heavy lines represent the sides and the ends of the pipe, while the urattsaiaa It can be noted in this case that the V dotted lines 2 represent the standing wave form present in the pipe for the resonant sound wave. At position O the pressure is greatest, Whic position corresponds to a nodal point, while at M an anti-node exists which represents a condition of maximum amplitude. Therefore, we have a condition where there is maximum amplitude at each end of the pipe which produces the greatest volume of sound.

The relationship of the diameter and length of the pipe l may be likened to the a a and b b axes of a piezo electric crystal. In the organ pipe theory there is an integral relationship between the amplitude or a a dimension and the lengthof b b dimension is a whole number relationship.

From this discussion We may consider that the integral relationship between a a and b b dimension has a reinforcing effect on the sound wave which causes a condition of maximum sound vibration Any decrease or increase in length along the b dimension'will change the reinforcing effect until another integral dimension is again obtained.

The same conditions stated with reference to the organ pipe are also met with in the crystals and it appears that the crystal pressure vibration conditions are identical to that of the organ pipe. Therefore, for maximum output from crystals it is imperative that the dimensions along the ca ai and b axes should be integrally related to each other.

In the drawings -we have shown the amount of material 3 whichis removed from the b b dimension ofthe crystal and `the amount of materiale which may be removed from the 0 d dimension 'of 'the crystal in greatly exaggerated sizeand it will be realized that the actual amount removed from Athe crystal may be infinitesimal along the c 0 axis after the b and ai cu dimensions have been fixed by grinding the faces of the crystals parallel to theiry geometrical axis to a mathematical ratio equal to a whole number.

In the construction of piezo electric crysit be understood that modifications may be made within the scope of the appended claims, without departing from the spirit of our invention.

lVhat we claim and desire to ksecure by Letters Patent of the United States is as follows:

l. A piezo electric quartz crystal having three sides disposed at right angles to each other, in which the axes are proportioned to each other in a ratio which is equal to a whole number for securing maximum piezo electric effect from said crystal.

2. A piezo electric quartz crystal in the form of a parallelopiped having a plurality of sides, in which the dimensions of two adjacent sides bear a whole number relationship to each other for securing the maximum piezo electric effect from said crystal.

3. A piezo electric quartz crystal having a plurality of sides extending at right angles to each other with a pair of said sides extending in a direction coincident with the optical axis of said crystal, said crystal having different dimensions along each 0f said 85 where bb represents the dimension along the lateral axis, and aa represents the dimension along the vertical axis is equal to an integer.

5. A piezo electric quartz crystal, comprislng a crystal having three sides disposed at right angles with respect to each other, with one of said sides positioned at a zero angle with respect to the optical axis of the crystalline body from which the crystal is cut` and the dimensions of the other sides having a mathematical ratio equal to a whole number.

6. A piezo electric quartz crystal in the form of a parallelopiped having a pair of faces substantially parallel to the optic axis and two other pairs of faces perpendicular to the first pair, said last mentioned pairs of faces having dimensions which are divisible one by the other to give a resultant equal to a whole number.

ALBERT H. TAYLOR. ALFRED CROSSLEY. 

